Conventionally, it is known that maleic acid copolymers as a polymer of water-soluble polycarboxylic acid (salts) having many carboxylic groups show excellent functions of chelation and dispersion. For these beneficial properties, such copolymers have been used in a variety of fields, such as a detergent builder of a detergent composition, a dispersant, a flocculating agent, a scale formation inhibitor, a chelating agent, and a fiber processing agent and the like.
Among the described copolymers, those having many carboxylic groups in each molecule are suitably used for the above-mentioned respective uses. In the process of manufacturing such maleic acid copolymers, to overcome the deficiency that the polymerizability thereof is generally low, it has been proposed to increase the amount of the maleic acid component to be placed in a polymerization process to introduce many carboxylic groups. However, such method has the following drawbacks.
(1) A still long time is required for the polymerization process because of the low polymerizability of the maleic acid component;
(2) When the maleic acid component is placed at a higher proportion, a greater amount of hydrogen peroxide (polymerization initiator) is required;
(3) The use of the hydrogen peroxide in a large amount results in a high content of residual hydrogen peroxide from the polymerization reaction; and
(4) In spite of the fact that the hydrogen peroxide (polymerization initiator) is used in a large amount, a content of residual unreacted maleic acid component is still high.
Furthermore, earnest researches have been made by the inventors of the present invention to find out important factors other than the content of the carboxylic acid of the maleic acid copolymer to improve the detergency of the detergent composition containing the maleic acid copolymer as a detergent builder.
As a result, the inventors of the present invention have found that it is important to improve the property of the maleic acid copolymer in its calcium ion stability constant, and the property against iron particle deposition for preventing clothes from being yellowish. Additionally, in the case of the maleic acid copolymers of high gelation properties, when using water of high hardness as water for washing, the detergency is significantly lowered as being undissolved. Thus, the inventors of the present invention have also found that it is necessary to lower the gelation properties.
As disclosed in the below-mentioned Gazettes, with the maleic acid copolymers produced under conventional reaction conditions, even if the hydrogen peroxide is used in a large amount as a polymerization initiator, it is difficult to effectively introduce the maleic acid component to a high molecular portion. Moreover, the problem of high content of residual unreacted maleic acid and hydrogen peroxide in the reaction solution upon the completion of the polymerization reaction has not been solved. Besides, the problem of high content of residual unreacted maleic acid and hydrogen peroxide remaining in the reaction solution upon completion of the polymerization reaction remains unsolved which results in low polymerizability.
The maleic acid copolymers isolated from the copolymerization reaction solution upon completion of the reaction have high concentration of hydrogen peroxide and a high content of the residual maleic acid, and maleic acid copolymers do not show desirable functions of chelation and dispersion. Therefore, such copolymers are not suited for the aforementioned purposes, and do not have sufficient levels of essential properties to improve the detergency of a detergent composition such as calcium ion stability constant, a property against iron particle deposition and a anti-gelation properties.
(1) Japanese Examined Publication No. 2167/1991 (Tokukohei 3-2167) discloses a process of manufacturing a maleic acid copolymer, wherein a maleic acid component is placed in a reaction vessel, and under the condition that the dropping of the maleic acid and the acrylic acid start and finish at the same time, a polymerization reaction of the maleic acid and acrylic acid is carried out at a pH in a range of from 3.5 to 5.0. The Gazette (1) discloses an example of using the maleic acid copolymer as a pigment dispersant. However, it fails to disclose the example of using an maleic acid copolymer as a detergent composition.
In the method of manufacturing the maleic acid copolymer of Gazette (1), a large amount of maleic acid in the reaction solvent remains unreacted upon completion of the reaction, and the hydrogen peroxide also remains unreacted in spite of the fact that a large amount of hydrogen peroxide water solution is used in the polymerization reaction. Additionally, the resulting maleic acid copolymer is inefficient in its calcium ion stability constant, property against iron particle deposition, anti-gelation properties, and the like.
(2) Japanese Laid-Open Patent Publication No. 218407/1987 (Tokukaisho 62-218407) discloses respective examples of using a maleic acid copolymers as a dispersant and a detergent composition. However, the detergent composition does not show an improved detergency from the generally used detergent composition, nor have desirably balanced properties for the detergent. The Gazette (2) discloses the process of preparing the maleic acid copolymer wherein a maleic acid component is placed in a reaction vessel, and under the condition that the dropping of the acrylic acid and hydrogen peroxide start and finish at the same time, a polymerization reaction is carried out at a pH of around 4-6, thereby obtaining a maleic acid copolymer.
In the method of manufacturing the maleic acid copolymer of Gazette (2), a large amount of maleic acid in the reaction solvent remains unreacted upon completion of the reaction in spite of the fact that a large amount of hydrogen peroxide is used in the polymerization process, and a large amount of hydrogen peroxide also remains unreacted. Besides, the resulting maleic acid copolymer is inefficient in its calcium ion stability constant, property against iron particle deposition property, anti-gelation properties, and the like.
(3) Japanese Examined Patent Publication No. 14046/1991 (Tokukohei 3-14046) discloses a copolymer of ethylenically unsaturated monomer and dicarboxylic acid. The Gazette (3) discloses an example of using such copolymer as a skin formation inhibitor with respect to the detergent but fails to disclose a concrete example of using such copolymer.
As in the case of the aforementioned Gazettes, the Gazette (3) discloses the process wherein the ethylenically unsaturated dicarboxylic acid component is placed in a reaction vessel, and a polymerization reaction is carried out under the condition that the dropping of the ethylenically unsaturated monocarboxylic acid and the hydrogen peroxide water solution start and finish at the same time. However, the resulting maleic acid copolymer is insufficient in its calcium ion stability constant, property against iron particle deposition, anti-gelation property, and the like.
As described, the maleic acid copolymers resulting from the conventional reaction process are inferior in essential properties for various uses especially as the detergent composition. In addition, it is difficult to remove the maleic acid and hydrogen peroxide remaining in the resulting maleic acid copolymer from the conventional reaction. Besides, when using the maleic acid copolymer having a large amount of the residual maleic acid as a detergent composition, chelating and dispersing functions are adversely affected, and the detergency is lowered. Furthermore, when using the maleic acid copolymer having a high content of residual hydrogen peroxide as a detergent composition, the problem of unsafety arises as it may adhere to a skin of the user.
In the case of using the above-mentioned conventional copolymer, for example, as a detergent builder for a detergent composition, it is preferable to use it in a powdered form rather than liquid form as it is less restricted in its density and mixing ratio. Besides, if the final product is in the powdered form, a cost required for the drying process of the product can be reduced.
However, such copolymer of a powdered form has the problem of uneasy handling due to its extremely high hygroscopicity and very poor fluidity, etc. Therefore, most copolymers available in the market are in liquid form rather than the powdered form.
The powdered detergent as the detergent composition is mainly available as a low density product resulting from the conventional spray-drying process. However, for convenience in view of transportation, carriage and storage place, etc., of the detergent, there is a tendency of using a compact powdered detergent of higher density.
The density can be increased, for example, in such a manner that a raw material is first formed into powders by the spray-drying process, and then formed into a granule by an agitated granulator such as a mixer as disclosed by (4) Japanese Laid-Open Patent Publication No. 2000/1994 (Tokukaihei 6-2000). For each step in the above-mentioned method, as at least one kind of liquid raw material is required, many processes of mixing, drying, granulating, drying, classification, etc., are required for each step.
On the other hand, when all the materials are in the powdered form, the detergent composition can be prepared only by the dry-mixing process, and the multiple-steps of mixing, drying, granulating, drying, classifying, and the like required in the Gazette (4) can be omitted. Namely, as the density can be increased by carrying out only one step of mixing, a significant cost reduction can be achieved.
However, the maleic acid copolymer used as one component of the detergent builder as one of the detergent composition has a problem of uneasy handling due to hygroscopicity when using it in the powdered form as previously described. Therefore, in practice, it is difficult to increase the density by applying the dry-mixing process to the detergent composition containing the copolymer.
In addition, when applying the dry-mixing process to a powder of each detergent composition, it is required to structure such that respective compositions have the same bulk density in consideration of the problem of segregation after mixing the powder. When applying the dry-mixing process to each composition of the powdered form, the fluidity of each powder is extremely important. Besides, in the mixing process, it is necessary to have low hygroscopicity of each powder to prevent it from adhering to a line, a hopper, and the like, and the bulk density thereof has to be set as close as that of the detergent composition.
However, as the copolymer has a desirable solubility to the washing water, it is difficult to satisfy the bulk density, fluidity and hygroscopicity sufficient for the dry-mixing process in the form of powder.